From: Adrian Freihofer <[email protected]>
Be more paranoid about compiler optimizations that can eliminate code
that is only used for debugger inspection.
scale_number() in cpp-example-lib.hpp: use 'volatile int scaled' to
prevent the compiler from inlining the function body away entirely,
which left no out-of-line address for a breakpoint.
cpp-example.cpp: initialize the std::vector from volatile variables so
the compiler cannot constant-fold the values and eliminate the for-loop
body. Pass numbers[0]+numbers[1]+numbers[2] (= 6) as the scale_number
argument to keep the vector live at the call site (exe_break_line=63);
the test assertion '$4 = 6' is unchanged since 1+2+3 == 6.
Update the test accordingly: exe_break_line moves from 56 to 63, the
LINE_SHIFT anchor changes to the volatile declaration line, and the
list-output assertion matches '{n1, n2, n3}'.
Note: the test was originally written to also check that the compiler
uses e.g. -O0 to avoid eliminating e.g. the vector, but that should
probably be tested separately. Changing this ide-sdk test to use
volatile variables is a more robust way to ensure the vector is not
eliminated, regardless of compiler flags.
Signed-off-by: Adrian Freihofer <[email protected]>
---
.../recipes-test/cpp/files/cpp-example-lib.hpp | 6 ++++--
.../recipes-test/cpp/files/cpp-example.cpp | 10 +++++-----
meta/lib/oeqa/selftest/cases/devtool.py | 17 +++++++++--------
3 files changed, 18 insertions(+), 15 deletions(-)
diff --git a/meta-selftest/recipes-test/cpp/files/cpp-example-lib.hpp
b/meta-selftest/recipes-test/cpp/files/cpp-example-lib.hpp
index d1c9bca416..5af30e2a79 100644
--- a/meta-selftest/recipes-test/cpp/files/cpp-example-lib.hpp
+++ b/meta-selftest/recipes-test/cpp/files/cpp-example-lib.hpp
@@ -15,10 +15,12 @@ struct CppExample
inline static const std::string test_string = "cpp-example-lib Magic:
123456789";
/* Header-only function, to exercise breakpoint resolution against
- * header-only debug info. */
+ * header-only debug info. volatile prevents compiler optimization from
+ * eliminating the function body, ensuring a concrete code location exists
+ * for debugger breakpoints. */
inline static int scale_number(int n)
{
- int scaled = n * 7;
+ volatile int scaled = n * 7;
std::cout << "scale_number(" << n << ") = " << scaled << std::endl;
return scaled;
}
diff --git a/meta-selftest/recipes-test/cpp/files/cpp-example.cpp
b/meta-selftest/recipes-test/cpp/files/cpp-example.cpp
index ad1abae257..a376419c13 100644
--- a/meta-selftest/recipes-test/cpp/files/cpp-example.cpp
+++ b/meta-selftest/recipes-test/cpp/files/cpp-example.cpp
@@ -50,17 +50,17 @@ int main(int argc, char* argv[])
sleep(1);
}
} while (endless_mode);
-
+ volatile int n1 = 1, n2 = 2, n3 = 3;
// Example: Demonstrate std::vector traversal for debugger inspection
- std::vector<int> numbers = {1, 2, 3};
+ std::vector<int> numbers = {n1, n2, n3};
std::cout << "Traversing std::vector<int> numbers:" << std::endl;
for (size_t i = 0; i < numbers.size(); ++i) {
std::cout << "numbers[" << i << "] = " << numbers[i] << std::endl;
}
- // Example: call a header-only function once, to exercise breakpoint
- // resolution against header-only debug info.
- CppExample::scale_number(6);
+ // Pass numbers elements as the argument so the compiler cannot eliminate
+ // the vector; 1+2+3 == 6, so the scale_number(n) check is unchanged.
+ CppExample::scale_number(numbers[0] + numbers[1] + numbers[2]);
return 0;
}
diff --git a/meta/lib/oeqa/selftest/cases/devtool.py
b/meta/lib/oeqa/selftest/cases/devtool.py
index 06be7ef2df..7338b85d7f 100644
--- a/meta/lib/oeqa/selftest/cases/devtool.py
+++ b/meta/lib/oeqa/selftest/cases/devtool.py
@@ -2975,8 +2975,8 @@ class DevtoolIdeSdkTests(DevtoolBase):
with open(cpp_example_cpp, 'r') as file:
cpp_code = file.read()
cpp_code = cpp_code.replace(
- " std::vector<int> numbers = {1, 2, 3};",
- extra_lines + " std::vector<int> numbers = {1, 2, 3};")
+ " volatile int n1 = 1, n2 = 2, n3 = 3;",
+ extra_lines + " volatile int n1 = 1, n2 = 2, n3 = 3;")
with open(cpp_example_cpp, 'w') as file:
file.write(cpp_code)
@@ -3016,7 +3016,7 @@ class DevtoolIdeSdkTests(DevtoolBase):
# the first _gdb_cross_debugging_multi call above.
self._gdb_cross_debugging_multi(
qemu, recipe_name, example_exe, MAGIC_STRING_NEW,
- exe_break_line=56 + LINE_SHIFT, exe_list_line=55 + LINE_SHIFT,
+ exe_break_line=63 + LINE_SHIFT, exe_list_line=55 + LINE_SHIFT,
hpp_break_line=21 + LINE_SHIFT, lib_break_line=31 + LINE_SHIFT)
def _gdb_cross(self):
@@ -3033,7 +3033,7 @@ class DevtoolIdeSdkTests(DevtoolBase):
self.assertIn("GNU gdb", r.output)
def _gdb_debug_cpp_example(self, magic_string, gdb_start_cmd="run",
- exe_break_line=56, exe_list_line=55,
hpp_break_line=21,
+ exe_break_line=63, exe_list_line=55,
hpp_break_line=21,
lib_break_line=31):
"""Get a series of gdb commands to debug the cpp-example-lib example"""
gdb_batch_cmd = " -ex 'break main' -ex '%s'" % gdb_start_cmd
@@ -3057,8 +3057,9 @@ class DevtoolIdeSdkTests(DevtoolBase):
# check if resolving std::vector works with python scripts
gdb_batch_cmd += " -ex 'list cpp-example.cpp:%d,%d'" % (exe_list_line,
exe_list_line)
- # Break on exe_break_line (the std::cout after the declaration) so the
- # vector constructor on exe_list_line has already run when GDB stops.
+ # Break on exe_break_line (the scale_number call) so the vector on
+ # exe_list_line is both constructed and referenced; the compiler cannot
+ # eliminate the vector because its elements are passed as the argument.
# These line numbers shift after the test inserts extra lines and
# recompiles, proving the breakpoint resolves via the freshly rebuilt
# debug info rather than a stale, cached line-to-address mapping.
@@ -3095,7 +3096,7 @@ class DevtoolIdeSdkTests(DevtoolBase):
# check if resolving std::vector works with python scripts
self.assertRegex(
- gdb_output, r"%d\s+std::vector<int> numbers = \{1, 2, 3\};" %
exe_list_line)
+ gdb_output, r"%d\s+std::vector<int> numbers = \{n1, n2, n3\};" %
exe_list_line)
self.assertIn("$3 = std::vector of length 3, capacity 3 = {1, 2, 3}",
gdb_output)
# check that a breakpoint in an inline function defined directly in
@@ -3106,7 +3107,7 @@ class DevtoolIdeSdkTests(DevtoolBase):
self.assertIn("exited normally", gdb_output)
def _gdb_cross_debugging_multi(self, qemu, recipe_name, example_exe,
magic_string,
- exe_break_line=56, exe_list_line=55,
hpp_break_line=21,
+ exe_break_line=63, exe_list_line=55,
hpp_break_line=21,
lib_break_line=31):
"""Verify gdb-cross is working
--
2.55.0
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